Large buildings must provide a safe path of egress for the occupants in case of fire. To achieve this, floors and walls are fire rated to prevent fire from traveling from one compartment or floor to another. To allow persons to escape the building, fresh air is also essential to prevent the occupants from being overcome by smoke while attempting to exit the building. To achieve this the ducts that are designed to deliver fresh air during a fire must be constructed so that even if the duct passes through a fire compartment that is fully engulfed in fire, the construction of the duct will withstand the effects of the fire and permit the continuous flow of fresh air to the persons evacuating the building.
An example of the application of fire rated duct system is a stair pressurization system which is typically mandated by building codes for high rise buildings. The stair pressurization system delivers a continuous supply of fresh air which: (a) supplies breathable air to the persons existing via the stairwell; (b) pressurizes the stairwell to prevent the passage of smoke from any floors exposed to fire conditions into the stairwell; (c) assists in removing any smoke that may have entered the stairwell during the opening and closing of doors.
Building codes in the United States and Canada require that products and systems used for fire protection systems are tested and listed by a recognized listing authority with most jurisdictions preferring UL/ULC.
Durasystems Barriers Inc., in Vaughan, Ontario, presently produces two listed fire-rated duct systems referenced as FRD-1 and FRD-2. The FRD-1 fire-rated duct system is a 2 hour UL/JLC Listed ventilation duct that is comprises of a support framework fabricated from ⅛″ (3 mm) thick steel that is welded into the required type of fitting and then clad with a fire resistant composite panel using specially tested fasteners. While effective in a fire, the FRD-1 duct system is expensive due to the labour involved in the manufacture of the product and its increased weight due to the thickness of steel required to support the panels make it less economical than many of the other competing products. The FRD-2 fire-rated duct system is a 2 hour ULC Listed duct and is similar to FRD-1 duct system in outer appearance but one of its principal applications is for use as a kitchen exhaust and solvent recovery duct system. The FRD-2 duct system comprises a double wall construction with a welded inner liner, an insulated cavity and FRD-1 as an outer casing. While effective in use where fire temperatures could reach high levels in a relatively short time, the additional weight of the inner liner and insulation as well as the additional fabrication costs resulting from the addition of the inner assemblies makes this system only practical for special applications.
A number of ceramic insulation manufacturers provide “wrap systems” that involve wrapping previously installed ventilation systems with one or two layers of ceramic insulation that has a foil scrim outer layer. Each insulation wrap is overlapped by the next wrap and sealed with foil backed tape to create a seal. Each end overlaps the starting end as well so that there is no butt seams in the system. Stainless steel bands are then wrapped around the outer layer of insulation which holds the insulation in place during a fire.
Perceived shortcomings of these systems include: (a) the need for multiple skilled tradesmen to install the finished system that can result in project scheduling issues; (b) ease of damage to the aluminum scrim outer coating that could result in a reduced fire resistance level and lead to the spread of ceramic fibers throughout the building; (c) the inability to ensure the system is correctly installed as per the factory guidelines; improper installation could result in a system offering little or no protection; (d) the thickness of the insulation wrap material results in an increased outer dimension for the duct work.
In the art, there are also systems that employ different types of fire resistant boards as a cladding which are installed after the ductwork is installed. Each board system has a different installation method which normally involves applying a mastic material to the edges of the boards to be joined and then nailing, stapling or banding the boards together to prevent separation in a fire. The drawback of such board systems include: (a) as with the insulation wraps, there is the need for multiple tradesmen to install the finished system which can result in project scheduling issues; (b) the fire-resistant cladding boards are subject to being damaged from impacts during or after installation; (c) the fire-resistant cladding boards are also susceptible to damage when exposed to high levels of moisture; (d) it is also not always possible to ensure installation of the fire-resistant cladding as per the manufacturers guidelines; and improper installation may result in a system offering little or no protection.
In view of the foregoing, there still remains a need for a fire-rated ducting system which overcomes shortcomings associated with the known systems.